Guided parasails 10, FIG. 1, provide a means of achieving precision delivery of supplies 12 from air 14 to ground 16. Guided parasails 10 are often static line deployed from an aircraft (not shown) at altitudes up to approximately 35,000 feet.
According to one embodiment, a guided parasail 10 includes a guidance system that outputs a heading rate command and a stability augmentation system (SAS) that follows (executes) that command. The guidance system typically includes an on-board flight computer that determines the position and heading of the parasail 10, usually based on a GPS and Inertial Navigation Sensors (INS) or the like. The guidance system regulates the altitude and heading of a parasail in such a way that it arrives at the target site at a prescribed altitude (very similar to the problem of landing an aircraft). The altitude profile (altitude versus range to the target site) depends both on wing loading, and wind magnitude and direction, both of which may be unknown at the outset.
Lightly wing-loaded parafoils 10 have basically a linear response to input control. At very high wing-loads, however, the response to input control becomes highly non-linear. Consequently, small input controls may result in large and undesirable responses. This is particularly problematic and can result in a spiraling descent from which there is no recovery (an instability). The difficulty in designing a SAS is that the nature of this nonlinearity (where it begins to happen and to what degree) is not known ahead of time because it depends on wing loading. Also, the behavior in turning in one direction may be different from the behavior in turning in another direction. Moreover, even if the nonlinearity was known, designing the control system would still be difficult because the state of the art in control system design relies heavily on having a linear response.
Accordingly, there exists a need for an improved SAS system that operates in the linear region. The system should take into account the physical limitations of the actuators/servos used to affect the controls as well as should limit the rate of turn to prevent entering the nonlinear region.
There also exists a need for an adaptive guidance system that is able to ascertain (estimate) the glide slope and wind conditions on the fly, and provide a command to the SAS that will result in attaining the desired glide slope and heading.
Moreover, there exists a need for an adaptive SAS system that operates in both the linear and the nonlinear region. This is due to the need to design intelligent, self-learning systems that enable users to adopt and deploy the equipment in the most practical manner. That is, there is a need to self adapt to a variety of drop conditions, payloads and wing loadings. Not doing this puts unneeded restrictions on users. These restrictions will often not be adhered to, sacrificing accuracy and reliability. An adaptive guidance and adaptive SAS design permits systems to fly correctly with asymmetrically rigged payloads or correct for damage-induced asymmetries mid-flight. Additionally, adaptive algorithms will permit varying cargo weights to be rigged under a given system, without any inputted data into mission planning.
It is important to note that the present invention is not intended to be limited to a system or method which must satisfy one or more of any stated objects or features of the invention. It is also important to note that the present invention is not limited to the preferred, exemplary, or primary embodiment(s) described herein. Modifications and substitutions by one of ordinary skill in the art are considered to be within the scope of the present invention, which is not to be limited except by the following claims.